This invention pertains to the art of can manufacturing and, more particularly, to an apparatus and method for lubricating the outside peripheral surface of a circumferential strip at the open end of a can.
The open end of a cylindrical metal can is commonly reduced in diameter and flanged. This process of reducing the diameter of a can is generally referred to as necking. The reduction in diameter lessens the amount of material needed for a closure and the flange facilitates attaching the closure to the can.
A common method of necking a can requires the employment of a necking die. A lubricant is applied to the outer peripheral surface of the circumferential strip at the open end of the can. The open end is then forced into the tapered necking die resulting in plastic deformation of the open end to a smaller diameter or neck. In a production line situation, a single necking die may perform this operation on over 800 cans per minute. Unless a sufficient lubricant coating is present on the outside surface of the can, substantial frictional forces will be generated in the necking operation. These frictional forces may result in excess die wear, generation of metal particles or fragments from the can, impact welding of the particles to the die, scratching of the can surface and in extreme cases, wrinkling, buckling, or fracturing of the can thereby producing an unusable can or causing production line stoppage. It is highly desirable to avoid even minor scratching of the flange portion of the can because of possible sealing problems when the end closure is attached. Also, it is to be understood that the metal cans herein disclosed are already decoratively coated by a primary coating such as paint, resin or the like and are thereafter brought into the process of the subject invention. Thus, the lubricant substantially aids in maintaining the integrity of the primary coating in the necking process. Purchasers of cans for packaging purposes insist that the integrity of this primary coating be maintained as it is considered a reflection on their product.
It is therefore imperative that sufficient lubricant coating be applied to the can. Although prior art apparatus and methods generally succeed in the application of a sufficient quantity of lubricant to the can, they are subject to a number of shortcomings.
Prior art lubrication apparatus have generally required the use of large quantities of an organic solvent as a carrier for the lubricant. Primarily, a hexane-lanolin or hexane-petrolatum mixture is used where the lubricant comprises about 2% of the mixture and the remainder is solvent. The mixture is applied to a container and the solvent rapidly evaporates leaving only the lubricant.
Hexane and other organic solvents so used are extremely flammable and pose a substantial health risk when used in the closed environment of a container manufacturing plant. A can line running at 850 cans per minute may use between 100 and 180 gallons of hexane per week, or up to 26 gallons per 24-hour period. Where there are two or more can lines in the same plant, the hexane used is proportionately increased. The advantages of eliminating hexane and other solvents from a lubrication system are apparent. Gallons of the substance are eliminated from the atmospheric environment and the cost of the solvent is avoided.
In the prior art the application of hexane-lubricant mixture is almost universally accomplished by various wicking devices. Besides usually requiring a volatile solvent as a carrier, the conventional wicking devices lack control over the quantity of lubricant applied to each can. This lack of control mandates that an excess of lubricant usually be applied to maintain an adequate margin of safety so that the above problems will be avoided.
The application of lubricant to the can by a wick system often involves some frictional forces between the can and the wick. A typical arrangement involves using dual belt drives, one on each side of the container, in conjunction with a long staionary wick. One belt drive rotates at a greater speed than the other. Due to the slower turning belt, the container is actually rotated at a greater speed than would be necessary for a pure rolling motion which results in the container being spun on the wick as well as translated along the wick's length. Most of the prior art wick systems involve some dragging or spinning of the container on the wick. This dragging necessitates a high standard of machine maintenance and adjustment.